I really like the concept of using game design. Although I've never had the opportunity to design a course myself, I have thought of courses in comparison to video games. In video gaming, games that are too easy and don't present a consistent challenge get boring very quickly. Likewise, games that seem unnecessarily difficult and present seemingly insurmountable challenges to advancement can turn a player off. A good balance of challenge, attainable obstacles and a sense of achievement keeps players coming back.

The most important concept which translates best to course design, is you want the player to feel in control of his own outcome. A player will become frustrated by a game if there is seemingly know way to defeat an obstacle other than sheer luck and timing (ie, maybe the guard will have his back turned when I come around the corner this time. Nope, I'm dead again). In terms of course design, placing trees or OB in the throwing line takes the control out of the players hands and lets the course dictate score (ie, well, I missed that tree this morning, hopefully I'll sneak by in the afternoon round too!).

While it may seem like an easy concept to grasp, it's very difficult to put into practice, especially over 18 holes.

This actually mirrors my own approach to course design exactly. I think there are a great many similarities between all forms of game design, and a lot of important features of good game design can be observed in good video games. In my non-disc-golf life, one of the things I do is teach a university course on video gaming for educators. To help teachers better understand how game-based learning works (or can work), one of the things I've been working on is attempting to classify the core elements present in all games (or more specifically in the activity we call 'gameplay'). I should mention up-front that there is no universally-accepted definition of a 'game'.. this is merely what I use. But I suspect that you'll spot the similarity of #5 below:

1). The player must feel that the activity rules or laws enable them to think, act, and value in unique (to the activity) and shared (across all activity participants) ways.

This is definitely the most universally-accepted element of 'games'. All games have rules, or more specifically, in all 'gameplay', participants agree to artificially limit themselves (for some benefit).

2). The player must have the opportunity to evaluate their performance, in relation to other players and the objectives of the activity.

Disc golf, like many other games and sports, provides numerous opportunities for the player to evaluate their performance. Most courses are at least 18 holes in length, typically averaging three throws per hole. You can evaluate your score/performance per throw, per hole, per course, and across courses very similarly. Further, as an individual sport, players are able to evaluate themselves solely based on their own performance, while at the same time observing the performance of others around them. Disc golf also utilizes the concept of 'par', by which a player can evaluate themself against an abstraction of how they 'should' perform.

3). The player must form goals relating to the desired outcome for the activity.

This one is actually less obvious than it sounds. What's really important here is that the cognitive process of goal-forming is individual to the player. A game or sport can present the player with many possible goals (#2 above), but in order for a a person to be engaging in gameplay, it's up to them to take on a goal or goals for themself. A new player might take on the goal of getting even 'par' for a hole or course.. or throwing x number of feet.. or maybe just throwing in the right direction each throw. A more advanced player might take on any number of goals for each throw, hole, course, etc.

It's also important to look at socially reinforced/accepted goals in disc golf, as the game learning community is often key in helping players with goal attribution. Players often take on goals related to an activity because they observe others in that community to be pursuing that same goal (i.e. the particular goal has value to the game community). Getting a 'birdie', for example, is heavily community-reinforced, and one of the primary reasons why I so strongly oppose a course design philosophy that allows for un-birdiable holes (at the target skill level, of course). By designing a hole that doesn't allow for birdies, you've just eliminated the most socially-reinforced and easiest-attributed goal in disc golf.

4). The player must not be able to predict or determine the precise outcome of the activity before engaging in it.

This is actually the key difference between 'games' and 'puzzles'. In a puzzle, you know what the final 'product' or outcome is going to be.. and the challenge is manipulating the pieces to get that outcome. The reason I bring this up is not to say that games are good and puzzles are bad, but that the reasons that a person engages in a game vs. a puzzle are not the same reasons. You see this all the time in video games.. as a player plays longer, and gets better at the game (or maybe has beaten it several times over), eventually they get to the point where the activity has no uncertainty anymore.. they're not going to die or fail, and they know exactly how everything will happen. That's usually the point when players stop playing, and move on to a new game.

With course design, this is the reason why I believe that examining the scoring spread for each hole is so critical, to ensure that each hole has sufficient (i.e. less than 70% the same) scoring distribution. The lower the scoring spread, the more like a 'puzzle' the hole/game becomes.. if you know exactly how you 'always' do on a hole, what's the point of 'playing' it?

5). The player must feel that, through their actions and decisions, they have some measure of control over the outcome of the activity.

You already talked about this one quite a lot, but I think it's important to mention that once again just how 'controllable' an activity needs to be in order for any specific individual to engage in 'gameplay' is of course different for each person. In general, as a players' skill increases, they expect to gain more and more control over the outcome of the activity. Good video games, for example, are often exceptional at this. As you get better at the game, you are frequently guided through experiences that reinforce the fact that you are now better at that activity (i.e. video games typically gradually increase in difficulty as player skill increases).

Controllability in disc golf (and sports in general) is often more of a challenge. Between the whims of wind, obstacles, and disc entrapment devices, there are plenty of times when players may feel like they have less control over the outcome of the activity than they should (which is what leads to anger, frustration, and players not 'playing' anymore). Good course design, though, should try to minimize this, and in my opinion there are lots of good ways to go about doing this. John Houck, for example, recently talked about how course 'obstacles' should in general be wider rather than skinny, to reduce the variability/randomness of outcome when the obstacle is struck.

As another example, I also like to apply rules about angular control when it comes to tight fairways and gaps. In my experience, most of the holes that players complain about as being 'unfair' or 'random' come from expecting players to be accurate to within too narrow of a deviation from the 'perfect' line.